Samtec recently completed an arduous flex and bend test on our Eye Speed® Ultra-Low Skew Twinax cable. This is used in our high speed cable assemblies, including the Samtec Flyover™ FQSFP-DD cable assembly. Besides achieving outstanding electrical performance, the testing has proved the cable to be rugged and provide stable electrical performance after repeated cycles.

QSFP-DD 101

QSFP-DD Double Density Pinout

QSFP-DD is a new module and cage/connector system similar to current QSFP, but with an additional row of contacts providing for an eight lane electrical interface. It is being developed by the QSFP-DD MSA as a key part of the industry’s effort to enable high-speed solutions. Samtec’s FQSFP-DD takes the Samtec Flyover™ architecture concept to the QSFP-DD form factor.

Samtec Flyover™

System Architects are now using an alternative signal path strategy – Samtec Flyover™ — that reduces the use of PCB traces to interconnect high-speed signals. Instead of increasing layer counts, using costly high-performance PCB materials, and dealing with long degrading trace lengths, the signals are taken out of the board and a cable is used to fly them over the PCB. We refer to this technique as Samtec Flyover. Samtec Flyover improves signal integrity performance, it allows for a higher signal speed, and it reduces the overall cost of the system.

There’s a lot that goes into making Flyover work: the contact design, the interface from the cable to the contact system, pcb routing strategies, and of course the cable itself. While every element is critical to the success of the interconnect system, the high-bandwidth cable is the differentiator in Samtec’s design. Samtec’s Ultra-Low Skew Eye Speed® co-extruded twinax cable technology eliminates the performance limitations and inconsistencies of individually extruded dielectric twinax cabling.

Fast, Flexible, Rugged Micro Twinax Cable

The Eye Speed twinax is not only fast, it’s rugged. We recently subjected our 34 AWG, 100 ohm twinax cable, the style commonly used in our FQSFP-DD series (and other Flyover applications), to a brutal Dynamic Insertion and Return Loss testing. In typical applications, mid-board and board-to-board high speed cables assemblies will not be subject to 250 or more flexes, and the real-life bends are not nearly as harsh as those performed in this Dynamic Test.

The following is a quick overview of the set-up:

In simple terms, the cable was coiled and uncoiled on mandrels (“rolling pins”).

Both ends of the cable were terminated; one end terminated to test boards and edge mount 2.92 connectors, the other was held stationary in a fixture.

A 4 ounce weight was attached to the opposite end as a static load.

The sample was wrapped around 1.35” (3.5 cm) mandrels. The mandrels freely rotate and move back and forth on a slide at a rate of 20-25 cycles/minute. One cycle equals one back and forth motion.

Cable sample length was 6 feet (1.83 meters).

The sample was connected to an Agilent N5230A 4 port VNA 20GHz range.

SOLT 4port eCal was completed prior to testing.

SDD11, SDD12, SDD21 and SDD22 was captured.

A baseline measurement was taken.

Dynamic data was recorded real time during flex cycling.

Test Results

Ultimately, predictable insertion loss is what matters most to system engineers. Many competitive twinax cables will function fine with their cable laid in a straight line, but bend them and performance changes drastically.

As the graphs below indicate, Samtec Eye Speed performance is stable after repeated cycles. After 250 flex/bend cycles, the performance of Samtec Eye Speed twinax is essentially indistinguishable from the original raw cable. This is a testament to the construction of our co-extruded foil-wrapped twinax design, which does not change performance within an application.

Eye Speed twinax provides the lowest insertion loss in the industry, controlled performance across temperature, and robust insertion loss in any assembly and operation environment.

For more information, including results at higher cycles, contact the HDR Group at Samtec.

Please note that test adaptors have not been de-embedded and losses are included in the displayed measurements

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